Handbook of Syn-thetic Photochemistry

Synthetic photochemistry is afascinating area of organic

chemistry and opens up a widevariety of unexpected routes to highly

complex families of products. Often, how-ever, these routes can also lead to unexpect-

edly complex reaction mixtures or can fail togive any conversion at all. This is mostly due to alack of awareness about the appropriate excitationmethod: whether by direct excitation or by triplet-energy transfer or electron transfer, choosing theright sensitizer or catalyst, and other reactionconditions. The Handbook of Synthetic Photo-chemistry, edited by Angelo Albini and MaurizioFagnoni, is a compilation of convincing examples ofthese diverse excitation routes and the necessaryreaction conditions. This handbook demonstratesthe potential of synthetic photochemistry, althoughone cannot expect it to present a comprehensivecollection of all known and synthetically relevantprocesses.

For work on synthetic photochemistry one hasto begin by considering basic technical and photo-physical conditions (solvents, irradiation reactorsand their geometries, lamps, sensitizers, quench-ers). These are discussed in a short introductorychapter (Albini), which also presents some basicretrosynthetic concepts for identifying photochem-ical processes. The first case study relates tophotodecarbonylation and photodecarboxylationof simple molecules in the solvent phase and inthe solid state (Garcia-Garibay). These processes,as well as photochemical addition to C�C multiplebonds (Fagnoni), are highly suitable for the for-mation of highly substituted C�C single bonds.

The photochemical synthesis of ring systemscovers 200 pages, and starts with the synthesis ofcyclopropanes (Tsuno). The main reactions for thistarget family are carbene additions, multistagecycloadditions, and rearrangement reactions. Forreactions to convert a compound into one ofgreater complexity (a concept that is, admittedly,not clearly defined), the di-p-methane (DPM)rearrangement and its oxa and aza variants, aswell as intramolecular meta-photocycloaddition toarenes, are ideal methods. The synthetic possibil-ities of the DPM rearrangement, as originallydeveloped by Zimmerman, are far from beingexhausted. By varying the reactive excited state(sensitization for transfer of energy and electronsas an alternative to direct excitation), by introduc-ing heteroatoms (1-oxa, 1-aza, 2-aza, etc.), or byvarying the reaction medium (solution versus solid-

state conditions, ionic liquids, chiral environments,zeolites, inclusion compounds) new reactivity pat-terns are continually being discovered, and evenopen-chain enones, which for many years weredescribed as unreactive, can be convinced to react.

As expected from orbital symmetry rules, thesynthesis of cyclobutanes and heterocyclobutanesare prime examples for photochemical reactions.Consequently, they appear in three different chap-ters and are described in detail with numeroustopical examples: addition of non-activated alkenesto arenes (ortho-photocycloaddition reactions) orto other alkenes (Hoffmann), addition of enones toalkenes or to other enones (Bach), and carbonyl-ene photocycloaddition reactions (Abe). Light-induced pathways to larger rings (Pandey, Perez-Prieto, Miranda) are usually initiated by intra-molecular H-abstraction or photoinduced electrontransfer steps. These processes are particularlyimportant for photochemical aromatic substitutionreactions that follow SRN1 and SN1 mechanisms(Arguello).

Chapter 11 deviates somewhat from the generalchapter structure, since it explicitly describes oneelectronically excited reagent, the first excitedsinglet state of molecular oxygen (Greer). This isdefinitely justified, as singlet oxygen not only showsa unique reactivity but also is ubiquitous undermany reaction conditions. This chapter is furtherdivided according to potential targets: dioxetanes,endoperoxides, allylic hydroperoxides, and theproducts of tandem photooxygenations. Also thispart of the book does not try to be comprehensive,but concentrates on significant examples and top-ical applications of the products of singlet oxygenphotooxygenations. Skeletal rearrangements ofheteroaromatic compounds, a group of reactionsthat are not easily controllable, are described inChapter 12 (Pace). Finally, the handbook is com-pleted by a highly topical description of photo-chemically switchable protection groups (Bochet).Especially in this area, light-induced reactions havereceived attention because light serves as a highlyspecific reagent to release functional groups.

The book describes many recent applications indifferent areas of organic photochemistry, with awealth of up-to-date literature references, and thatmakes it especially valuable and interesting for allsynthetic chemists.

Axel G. GriesbeckDepartment of ChemistryUniversity of Cologne (Germany)

DOI: 10.1002/anie.201003164

Handbook of SyntheticPhotochemistryEdited by Angelo Albini andMaurizio Fagnoni. Wiley-VCH, Weinheim 2009.464 pp., hardcoverE 139.00.—ISBN 978-3527323913

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5033Angew. Chem. Int. Ed. 2010, 49, 5033 � 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim